Endoluminal prostheses are typically used to repair, replace, or otherwise correct a diseased or damaged blood vessel. An artery or vein may be diseased in a variety of ways. The prosthesis may therefore be used to prevent or treat a wide variety of defects such as stenosis of the vessel, thrombosis, occlusion, or an aneurysm and dissections.
One type of endoluminal prosthesis used in treatment and repair of diseases in various blood vessels is a stent. A stent is a generally longitudinal tubular device which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. Endovascular stents have become widely used for the treatment of stenosis, strictures, and aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel.
Stents are generally open ended and are radially expandable between a generally unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded insertion diameter. Stents are often flexible in configuration, which allows them to be inserted through and conform to tortuous pathways in the blood vessel. The stent is generally inserted in a radially compressed state and expanded either through a self-expanding mechanism, or through the use of balloon catheters.
A graft is another type of endoluminal prosthesis which is used to repair and replace various body vessels. Whereas a stent provides structural support to hold a damaged vessel open, a graft provides an artificial lumen through which blood may flow. Grafts are tubular devices which may be formed of a variety of materials, including textile and non-textile materials natural and synthetic. Grafts also generally have an unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded diameter. The graft is sutured to the lumen to secure it in place.
It is also known to use both a stent and a graft to provide additional support for blood flow through weakened sections of a blood vessel. In endovascular applications the use of a stent and a graft is becoming increasingly important because the combination not only effectively allows the passage of blood therethrough, but also ensures the implant will remain open and provides containment of the blood. Sealing significantly reduces the transmission of arterial pressure through to the diseased segment.
The use of both a stent and a graft is available in various forms. One such form is a stent-graft composite where the stent is cast onto or imbedded into a graft, leaving the graft inseparable from the stent, as described in U.S. Pat. No. 6,156,064 to Chouinard. Another stent-graft form is a multi-stage stent graft, such as those described in U.S. Pat. No. 5,122,154 to Rhodes, and U.S. Pat. No. 5,578,071 to Parodi. A graft and the stent can be attached or unattached to each other. The graft is anchored/fixed to the vascular wall by the deployment of a stent inside the graft (endoskeletal) which sandwiches the graft between the vascular wall and the stent.
The deployment of multi-stage stent graft is complex because of the different expansion properties between the graft and the stent, and the frictional relationship between the two in the delivery sheath. As the stent expands within the graft, irregular expansion of the graft may occur, provoking graft deformities, such as creases or folds, on the graft that act as constrictor rings to limit the expansion of the stent.
The micro motion of the stent expanding inside the graft can produce distal migration of the graft material. An obstruction of blood flow is experienced when the stent covered graft is initially deployed. Deployment of the stent-graft is not instantaneous, rather, it is deployed in a piece by piece manner. As the stent-graft begins to expand from its proximal target zone, it naturally “flows open” and thus is subject to the arterial pulsatile flow. The blood cannot flow through the graft, creating retrograde pressure. The retrograde pressure, caused by the obstruction of blood flow, causes the graft to twist, crumble and not properly unfold, and the stent may not anchor properly, move or shift during or after deployment. Primarily, the arterial pulsatile flow acts upon the stent-graft, and if sufficient traction has not developed between the stent-graft and vessel, causes detrimental distal movement. Importantly, this affects the proximal deploy/placement accuracy.
Retrograde pressure is also experienced where the stent-graft is partially covering an outlet vessel, creating an obstruction of blood flow from the feed vessel to the outlet vessel. The blood begins to back up within the feed vessel, leading to other complications. The stent-graft cannot be repositioned, once the graft is partially or fully deployed beyond the point of being able to be repositioned, and sandwiched between the stent and the artery wall, without damaging the stent-graft or possibly injuring the artery wall.
Thus, there is a need in the art for an endoluminal prosthesis placement that eliminates such problems associated with concurrent deployment of a stent and graft, and blood flow obstruction. There is a need for an endoluminal prosthesis that is least obstructive to the blood flow upon deployment and modular assembly. The endoluminal prosthesis must also allow for selective cellular ingrowth, provide reliable prosthesis fixation, long term durability and allow for post-deployment adjustments/anatomical evolution.